1. Field of the Invention
The present invention relates to a control unit and a control method for an electric vehicle, and in more detail, relates to a control unit for an electric vehicle capable of being driven using at least torque from an electric motor.
2. Related Art
As a control unit for an electric vehicle, in an electric vehicle that travels under torque from an electric motor, there has been proposed a device for controlling vibration of a vehicle using feed-forward control taking into consideration disturbance torque (for example, Japanese Patent Laid-open No. 2000-217209). This device is provided with a plant model having a transfer function that approximates to the transfer function of an actual plant, feed forward control means using an inverse function of this plant model transfer function to set electric motor torque, and inputting the set torque to an actual plant side and to the plant model, and compensation means for estimating disturbance torque based on a deviation between an output value of the actual plant and an output value of the plant model, and compensating electric motor torque input to the actual plant side from the feed forward control means using this estimated disturbance torque, and unavoidable disturbance torque that can not be removed by feed forward control is removed using the plant model.
However, with this type of electric vehicle control unit, feed back control is also carried out, in addition to feed forward control, which means that the amount of processing required to carry out control becomes significant, and it is not possible to use a CPU that has a slow operation speed.
Further, application of this control device is limited to vehicles that travel under torque from an electric motor, which means that in the case of application of control to suppress vibration to a hybrid vehicle traveling under torque from an internal combustion engine and an electric motor, torque output from the internal combustion engine will incorrectly be processed as disturbance torque. Thus it is not possible to suppress vibration induced by the torque output from the internal combustion engine.
One advantage of the electric vehicle control unit and control method of the present invention is that there is control of vibration accompanying vehicle torque variation regardless of whether of not there is an internal combustion engine. Another advantage of the electric vehicle control unit and control method of the present invention is that there is control of vibration accompanying variation in vehicle torque using control that requires a reduced amount of computation.
The electric vehicle control unit and control method of the present invention have the following means in order to achieve at least some of the above described advantages.
A control unit of the present invention for an electric vehicle capable of being driven using at least torque from an electric motor comprises electric motor rotation speed detection and estimation means for detecting or estimating rotation speed of the electric motor, drive wheel rotation speed detection and estimation means for detecting or estimating rotation speed of drive wheels, and torque instruction compensation means for compensating an electric motor torque instruction so as to control vibration of the vehicle based on rotational speed of the electric motor detected or estimated by the electric motor rotation speed detection and estimation means and drive wheel rotation speed detected or estimated by the drive wheel rotation speed detection and estimation means.
With this electric vehicle control unit of the present invention, vehicle vibration is suppressed by compensating the electric motor torque command based on detected or estimated electric motor rotation speed and drive wheel rotation speed. Since this is control with calculation using electric motor rotation speed and drive wheel rotation speed, it is possible to reduce the amount of computation required for control compared to using control that carried out feedback control in addition to feed forward control. As a result, it is possible to use a CPU with a slow operation speed.
In this type of electric vehicle control unit of the present invention, it is also possible for the torque instruction compensation means to have means for compensating the torque by subtracting a compensation value obtained by multiplying a rotational speed difference between derived rotational speed of the drive wheels derived from detected or estimated electric motor rotation speed, and the detected or estimated drive wheel rotation speed, by a specified gain, from the torque instruction. In the electric vehicle control unit of this aspect of the present invention, the specified gain can be determined so that poles of a characteristic equation for a pair of simultaneous equations, namely an equation of motion for the drive system of the electric vehicle described above, with the electric motor rotational speed, the drive wheel rotational speed and a drive shaft twist angle as variables, and an equation of state for the control system using the above described electric motor input torque obtained by subtracting the rotational speed deviation, multiplied by the gain, from the torque instruction, become real numbers.
Also, in the electric vehicle control unit of the present invention, it is possible for the drive wheel rotation speed detection and estimation means to have means for estimating rotational speed of the drive wheels based on at least the electric motor rotation speed and the compensated torque command input to the control system.
Further, in the electric vehicle control unit of the present invention, it is possible for the electric motor rotation speed detection and estimation means to have means for estimating the electric motor rotation speed based on the electric motor rotation speed detected at low resolution, and the compensated torque command input to the control system.
Alternatively, it is possible, in the electric vehicle control unit of the present invention, to provide disturbance estimation means for estimating disturbance based on a torque command compensated by the torque command compensation means, a derived rotational speed of the drive wheels derived from detected or estimated rotation speed of the electric motor, and a detected or estimated drive wheel rotation speed, and it is possible for the torque instruction compensation means to be compensation means for compensating the torque instruction based on disturbance estimated by the disturbance estimation means. In this way, it is possible to effectively suppress vehicle vibrations due to disturbance.
In a control unit for a hybrid electric vehicle of the present invention capable of being driven using torque from an internal combustion engine having an aspect for estimating rotation speed of drive wheels and rotation speed of an electric motor, there is provided output torque estimation means for estimating output torque of the internal combustion engine, and it is possible for the drive wheel rotation speed detection and estimation means to have means for estimating drive wheel rotation speed based on output torque estimated by the output torque estimation means.
In the electric vehicle control unit of the present invention having an aspect where drive rotation speed is rotated based on the estimated internal combustion engine output torque, it is possible for the electric motor rotation speed detection and estimation unit to have means for estimating electric motor rotation speed based on output torque estimated by the output torque estimation means.
In the electric vehicle control unit of the present invention having an aspect where disturbance estimation means is provided and drive wheel rotation speed is estimated based on estimated internal combustion engine output torque, it is possible for the disturbance estimation means to have means for estimating disturbance based on output torque estimated by the output torque estimation means.
A control method for an electric vehicle of the present invention, being a control method for an electric vehicle capable of being driven using torque from at least an electric motor, comprises the steps of:
(a) detecting or estimating electric motor rotation speed and drive wheel rotation speed; and
(b) compensating a torque command for the electric motor so as to suppress vehicle vibration based on the detected or estimated electric motor rotation speed and drive wheel rotation speed.
With the electric vehicle control method of the present invention, it is possible to suppress vehicle vibration by compensating an electric motor torque command based on detected or estimated electric motor rotation speed and drive wheel rotation speed. Also, since control involves computation using the electric motor rotation speed and drive wheel rotation speed, it is possible to reduce the amount of computation required for control compared to control where feedback control is carried out in addition to feed forward control. It is therefore possible to carry out control using a CPU with a slow operation speed.
In the control method for an electric vehicle of the present invention, it is possible for step (b) to be a step of compensating the torque instruction by subtracting a compensation value, obtained by multiplying a rotational speed deviation between appropriate speed of detected or estimated rotational speed of the electric motor appropriate for the drive wheels and detected or estimated drive wheel rotational speed by a specified gain, from the torque instruction. In this aspect of the electric vehicle control method of the present invention, it is possible for step (b) to be a step of using the gain determined so that poles of a characteristic equation for an equation of state for the control system using an equation of motion for the drive system of the electric vehicle described above, with the electric motor rotational speed, the drive wheel rotational speed and a drive shaft twist angle as variables, and the above described electric motor input torque obtained by subtracting the rotational speed deviation, multiplied by the gain from the torque instruction, become real numbers, as the specified gain.